Method of making rotor and stator pole assemblies by stamping magnetic plate

ABSTRACT

Complementary laminations for a stator pole assembly and a cooperating rotor pole assembly of an electric motor or generator are produced simultaneously from a plate of magnetic material. The plate is stamped to produce an outer peripheral edge corresponding in shape to the exterior of an annular stator yoke and to produce a central aperture shaped to be received by an indexing element of an indexing table. The plate is then repeatedly indexed about its center in equal angular increments and a punch is displaced in a reciprocating rectilinear fashion synchronized with the indexing to punch a multiplicity of identical apertures equally-spaced circumferentially. The apertures are shaped to define internal edge surfaces in the plate corresponding in shape to radially inner surface of the stator yoke and to radially outer surfaces of a central hub of the rotor pole assembly and to define a multiplicity of identical radial webs. The multiplicity of webs is cut with a circular punch such that the plate is divided into a stator pole assembly lamination with radially-inward projections corresponding in shape to stator poles and a rotor pole assembly lamination with radially-outward projections corresponding in shape to rotor poles.

FIELD OF THE INVENTION

The invention relates to the construction of electric motors andgenerators, and, more particularly, to methods of manufacturinglaminated stator and rotor pole assemblies for such machines.

BACKGROUND OF THE INVENTION

The invention has particular, though not exclusive, application toswitched reluctance motors. Such motors generally comprise stator androtor pole assemblies formed of laminated sheets of magnetic material,typically motor iron. For purposes of this specification, the term"magnetic material" should be understood as a material appropriate forconduction of the magnetic fluxes necessary for motor or generatoroperation.

Switched reluctance motors are constructed in a variety ofconfigurations. A stator pole assembly may have several poles integrallyformed with a yoke that serves to complete magnetic paths between thepoles as well as providing structural support. Often the stator will beformed of several separate and distinct stator pole assemblies; that is,the stator has a multi-unit construction. Alternatively, the stator mayhave a single annular yoke to which all stator poles are attached. Therotor may have a central hub with rotor poles extending radially awayfrom the hub. Alternatively, the rotor poles may be bars of magneticmaterial effectively embedded or fastened within a rotating supportstructure. The rotor and stator poles may be equal in number, butdifferences in number and consequently pitch are more common to permitself-starting of the motor.

Regardless of configuration, the rotor and stator pole assemblies willhave a laminated construction to reduce eddy currents. The laminationsare often made by stamping plates of magnetic material in an appropriateshape. The stamping process may require separate treatment for rotor andstator pole assemblies, the complexity of the operation being dependentin part on motor design. Complex progressive stamping may be required,and those skilled in the art will appreciate the very significant costinvolved in providing appropriate stamping equipment.

Those skilled in the art will appreciate that there is littledistinction in the general construction or configuration of motors andgenerators. The latter generally comprise stator and rotor laminations.The teachings of this specification, although focussed primarily onmotors, should be understood as having application to the constructionof both motors and generators (including alternators).

SUMMARY OF THE INVENTION

The invention provides inter alia a convenient method for making astator pole assembly and a cooperating rotor pole assembly, particularlythe laminations that constitute such motor or generator components. Themethod involves a combination of stator/rotor configuration andmanufacturing steps that permit overall manufacture to be simplified.The configuration to be observed involves a stator assembly having anannular yoke and a multiplicity of poles directed radially-inwardly fromthe yoke, a rotor configuration having a central hub and a multiplicityof rotor poles directed raidally-outwardly from the hub, and equalnumbers of rotor and stator poles. The method of the invention permits asheet of magnetic material to be conveniently punched to definecomplementary pairs of stator and rotor laminations.

In one aspect, the invention provides a method of making a stator poleassembly and a cooperating rotor pole assembly which involves producinga predetermined number of complementary rotor and stator pole assemblylaminations. Each complementary pair of laminations is produced bystamping a plate of magnetic material to define an outer peripheral edgecorresponding in shape to the outer peripheral surface of an annularstator yoke and to define therein a central aperture, preferably with asingle pass of an appropriate punch. The plate is punched to define amultiplicity of apertures of predetermined identical shape, equallyspaced circumferentially and at a common radial distance from a centerpoint of the plate. The predetermined shape is selected such that theapertures define internal edge surfaces in the plate corresponding inshape to radially inner surfaces of the stator yoke and to radiallyouter surfaces of a central hub of the rotor pole assembly. Theapertures also define a multiplicity of identical radial websequally-spaced circumferentially. The multiplicity of webs are stampedto produce a cut through each web with a common predetermined radius ofcurvature relative to the center point of the plate, preferably with asingle circular punch. This results in the plate being divided into astator pole assembly lamination with radially-inward projectionscorresponding in shape to required stator poles and a complementaryrotary pole assembly lamination with radially-outward projectionscorresponding in shaped to the required rotor poles. To completeassembly, the stator pole assembly laminations are mounted inregistration and in side-by-side relationship on an appropriate supportstructure (such as a cylindrical casing) to form the stator poleassembly. The rotor pole assembly laminations are mounted inregistration and in side-by-side relationship on a support shaftextending through their central apertures to form the rotor poleassembly. The support shaft is mounted for rotation relative to thesupport structure with the rotor pole assembly positioned centrallywithin and substantially coplanar with the stator pole assembly.

In connection with the stamping of each plate to define its multiplicityof identical apertures, the central aperture punched into each plate maybe shaped to interfit with an indexing element of an indexing table.Thereafter, a multiplicity of identical apertures are produced byrepeatedly indexing the plate by preselected angular increments about apredetermined indexing axis through its center point, and producing areciprocating rectilinear displacement of an appropriately configuredpunch along an axis parallel and offset from the indexing axis.

The advantage of the method of the invention is that complementawrystator and rotor pole assembly laminations can be produced very simplyand without resort to more costly and complicated processes ofprogressive stamping. This ultimately reduces the cost of an electricmotor or generator.

Other aspects of the invention will be apparent from a description belowof a preferred embodiment and will be more specifically defined in theappended claims.

DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to drawings inwhich:

FIG. 1 is a diagrammatic side elevational view of a first stage of astamping process for producing complementary stator and rotor poleassembly laminations; and,

FIG. 2 is a plan view of the product produced by the first stage of theprocess;

FIG. 3 is a diagrammatic side elevational view, partially cross-section,of apparatus for implementing a second stage of the process, involvingrepeated indexing and stamping of the product of the first stage;

FIG. 4 is a plan view of the partially-completed product of the secondstage of operation;

FIGS. 5 and 6 are plan views showing the finished pair of complementarylaminations after a final stamping process; and,

FIG. 7 is an exploded perspective view indicating the generalconfiguration of an exemplary electric motor incorporating stator androtor pole assemblies constructed according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is made to FIG. 7 which illustrates an exemplary switchedreluctance motor 10 constructed according to the methods of the presentinvention. The motor 10 has been extensively fragmented to highlight itsstator and rotor pole assemblies 12, 14, the more significant componentsof the present invention. The stator pole assembly 12 is mounted withinan outer cylindrical casing 16 and comprises an annular yoke 18 withradially-inwardly directed poles (only one such pole 20 beingspecifically indicated) equally-spaced circumferentially about theinterior of the yoke 18. The rotor pole assembly 14 is locatedsubstantially coplanar with the stator pole assembly 12. The rotor poleassembly 14 is mounted by means of its central apertured hub 22 to arotatable shaft 24 for rotation relative to the stator pole assembly 12,as required for motor 10 operation, and has a multiplicity of rotorpoles (only one rotor pole 26 being specifically indicated) which extendradially outwardly from the hub 22. It will be noted that there areequal numbers of rotor and stator poles with the same pitch (angularseparation). Coils are mounted on the stator poles, such as theexemplary coil 28, and appropriate controls are provided to switchcurrent flows to produce motor action.

What is illustrated is in fact a single stage motor which would requirea starter motor. However, self-starting may be provided by using amulti-stage construction, each stage being substantially identical toand axially aligned with the stage illustrated, and arranging for therotor or stator poles of successive stages to be angularly offset sothat at least one stage is capable of providing motor action at anygiven time. Other details regarding construction and operation of such amotor 10 will be readily apparent to those skilled in the art and willnot be described.

As apparent in FIG. 7, both the stator and rotor pole assemblies have alaminated construction. The first stage of an exemplary process forproducing the required laminations will be described with reference toFIGS. 1 and 2. A plate 30 of magnetic material is supplied to a stampingmachine. The plate 30 is positioned between a punch 32 and acomplementary die 34, and below a conventional stripping plate 36 thatensures separation of the plate 30 from the punch 32. The punch 32 isshaped so that a single pass against the motor 10 material imparts anouter peripheral edge 38 corresponding in shape to the outer peripheralsurface 40 of the yoke 18 and also defines a central aperture 42, asapparent in FIG. 2, where the plate 30 as processed to this stage isshown. The central aperture 42 is centered about the center point 44 ofthe plate 30 and may be seen to comprise a multiplicity of recessesequally spaced about its periphery, only one such recess beingspecifically indicated with reference numeral 46. These recesses arecomplementary to splines (such as the spline 48) formed on the exteriorof an indexing element 50 of a conventional indexing table 52.

The plate 30 is then mounted on the indexing table 52 with the indexingelement 50 operatively located within the central aperture 42 of theplate 30, as apparent in FIG. 3. The plate 30 is indexed about anindexing axis 54 through the center point 44 of the plate 30 in equalangular increments (30 degrees in this particular embodiment of theinvention). A punching element 56 is supported for reciprocatingrectilinear movement along an axis 58 parallel to and offset from theindexing axis 54. In response to each indexing of the plate 30, thepunching element 56 is driven against the plate 30 and a complementarydie to produce an aperture of a predetermined shape, roughly a rounded,pie-shaped sector. An aperture indicated with the reference numeral 60is exemplary. The synchronizing of the displacement of the punchingelement 56 with the indexing of the plate 30 is conventional and willconsequently not be described further.

The indexing and punching continue until twelve identical apertures,equally spaced circumferentially at a common radial distance from thecenter point 44 of the plate 30 are produced. It should be noted thatthe shape of the apertures is such that they define internal edgesurfaces in the plate 30 corresponding in shape to the radially innersurfaces of the stator yoke 18 and the radially outer surfaces of thecentral hub 22 of the rotor pole assembly 14. One exemplary internaledge surface 62 (indicated in FIG. 4) corresponds to a radially innersurface 64 (indicated in FIG. 7) of the stator yoke 18. An exemplaryinternal edge surface 66 (indicated in FIG. 4) corresponds to a radiallyouter surface 68 (indicated in FIG. 7) of the central hub 22. Theapertures are otherwise shaped to define twelve identical radial websequally-spaced circumferentially and each having largely parallel sideedges. One such web is specifically indicated with reference numeral 70in FIGS. 4-5. These webs will ultimately constitute lamination portionscorresponding to rotor and stator poles.

The plate 30 is then punched with a circular punch to produce the plateconfiguration apparent in FIG. 5. Since such punching is entirelyconventional, the punching element and complementary die required forsuch purposes have not been illustrated. This punching step produces acut through each web at a common predetermined radius of curvaturerelative to the center point 44 of the plate 30, all webs being cutsimultaneously in this particular embodiment of the invention. Thecommon radius of curvature of the cuts ensures that the rotor will beconfigured to rotate freely within the stator. This also divides theplate 30 into a stator pole assembly lamination 72 with radially-inwardprojections (such as the projection 74 indicated in FIG. 6) thatcorrespond in shape to the required stator poles and a complementaryrotor pole assembly lamination 76 with radially outward projects (suchas the projection 78 indicated in FIG. 6) that correspond in shape tothe required rotor poles. It will be apparent that the punching processcan easily be adapted to produce any required clearance (air gap)between stator and rotor poles in the resulting motor.

The process steps described above are repeated until a desired number ofcomplementary laminations are produced. The stator pole assemblylaminations are then registered in side-by-side relationship (theorientation of FIG. 7). They may be held in such an orientation in anappropriate jig and welded permanently together. The recesses in theouter peripheral edge of the stator laminations (such as the exemplaryrecess 80 indicated in FIGS. 2-6) align to define channels along whichweld beads can conveniently be provided. Also, an elongate key-likebridging element (not illustrated) can be placed in each such channel tospan the distance between the stator pole assembly 12 and the outercasing 16 to permit the stator pole assembly 12 to be fixed relative tothe outer casing 16 by appropriate welding of the bridging element. Anyappropriate means can be used, however, to keep the laminations inregistration and to mount the stator pole assembly 12 to the casing 16.

The rotor pole assembly laminations are registered and mounted inside-by-side relationship on the support shaft 24 as in FIG. 7. Therecesses associated with their central apertures are aligned and used tokey the assembly onto the support shaft 24 for rotation with the shaft24. More specifically, the rotor pole assembly laminations are fittedonto an enlarged portion 82 of the shaft 24, formed with severallongitudinal key channels. They are retained in such a configuration atopposite ends thereof by a pair of retaining plates (only one suchretaining plate 84 being apparent in FIG. 7) which are apertured to fitabout the enlarged portion 82 of the shaft 24. The plate 84 may have aninternal spring-biased key (not illustrated) which fits into a circulargroove 86 formed in the enlarged portion 82 of the shaft 24 oralternatively a C-ring or other fastening means (not illustrated) can beused (with the position of the circular groove 86 adjusted accordingly).These matters are conventional and will not be described further. Theshaft 24 is bearing mounted in a conventional manner by a pair ofbearing (such as the exemplary bearing 88), the bearings being bolted toa pair of opposing end plates (such as the plate 90) fitted to theaxially-opposite ends of the casing 16. Other details regarding assemblyof the motor 10 are conventional and will not be descirbed.

It will be appreciated that a particular embodiment of the invention hasbeen described and that modifications may be made therein withoutdeparting from the spirit of the invention or necessarily departing fromthe scope of the appended claims. A variety of modifications to theprocess might be considered. For example, rather than using a circulardie to cut the webs, the punch otherwise used to produce themultiplicity of pie-shaped apertures may simultaneously cut one of thewebs as each new apertured is punched.

I claim:
 1. A method of making a stator pole assembly and a cooperatingrotor pole assembly for an electric motor or generator,comprising:producing a predetermined number of complementary rotor andstator pole assembly laminations by repeating the following steps:A.providing a plate of magnetic material, B. stamping the plate therebydefining an outer peripheral edge corresponding in shape to an outerperipheral surface of an annular stator yoke, C. stamping the platethereby defining a central aperture centered about a center point of theplate, D. stamping the plate thereby defining a multiplicity ofapertures of predetermined identical shape equally-spacedcircumferentially and at a common radial distance from the center pointof the plate, the predetermined shape being selected such that themultiplicity of apertures define internal edge surfaces in the platecorresponding in shape to radially inner surfaces of the stator yoke andto radially outer surfaces of a central hub of the rotor pole assemblyand define a multiplicity of identical radial webs equally-spacedcircumferentially, and E. stamping the multiplicity of webs therebyproducing a cut through each web with a common predetermined radius ofcurvature relative to the center point of the plate such that the plateis divided into a stator pole assembly lamination with radially-inwardprojections corresponding in shape to stator poles and a rotor poleassembly lamination with radially-outward projections corresponding inshape to rotor poles; mounting the stator pole assembly laminationsregistered and in side-by-side relationship on a support structurethereby forming the stator pole assembly; mounting the rotor poleassembly laminations registered and in side-by-side relationship on asupport shaft extending through the central apertures of the rotor poleassembly laminations thereby forming the rotor pole assembly; mountingthe support shaft for rotation relative to the support structure withthe rotor pole assembly positioned centrally within and substantiallycoplanar with the stator pole assembly.
 2. The method of claim 1 inwhich:the stamping in step C further comprises shaping the centralaperture of the plate such that the plate interfits with an indexingelement of an indexing table; and, the stamping in step D comprisesproviding a punch shaped to produce apertures of the predeterminedshape, interfitting the plate with the indexing element of the indexingtable and repeatedly indexing the plate by preselected angularincrements about a predetermined indexing axis through the center pointof the plate, and producing a reciprocating rectilinear displacement ofthe punch synchronized with the indexing of the plate and directed alongan axis parallel to and offset from the indexing axis.
 3. The method ofclaim 2 comprising providing a punch having stamping surfacescorresponding in shape both to the outer peripheral surface of thestator yoke and to the central aperture and performing the stamping insteps B and C with a single pass of the punch against the plate.
 4. Amethod of making a stator pole assembly and a cooperating rotor poleassembly, comprising:producing a predetermined number of complementaryrotor and stator pole assembly laminations by repeating the followingsteps:A. providing a plate of magnetic material, B. stamping the platewith a single pass of a first stamping element thereby defining an outerperipheral edge corresponding in shape to an outer peripheral surface ofan annular stator yoke and a central aperture centered about a centralpoint of the plate and having a shape complementary to an indexingelement of an indexing table; C. mounting the plate on the indexingtable with the indexing element operatively located within the centralaperture and repeatedly indexing the plate in equal angular incrementsabout a predetermined indexing axis through the center point of theplate; D. stamping the plate with a second stamping element supportedfor reciprocating rectilinear movement along an axis parallel to andoffset from the indexing axis in response to indexing of the plate suchthat a multiplicity of identical apertures of a predetermined shape areformed in the plate, equally spaced circumferentially and at a commonradial distance from the center point of the plate, the predeterminedshape being selected such that the multiplicity of apertures definesinternal edge surfaces in the plate corresponding in shape to radiallyinner surfaces of the stator yoke and radially outer surfaces of acentral hub of the rotor and define a multiplicity of identical radialwebs equally-spaced circumferentially, and E. stamping the multiplicityof webs thereby producing a cut through each web with a commonpredetermined radius of curvature relative to a center point of theplate such that the plate is divided into a stator pole assemblylamination with radially-inward projections corresponding in shape tostator poles and a rotor pole assembly lamination with radially-outwardprojections corresponding in shape to rotor poles; mounting the statorpole assembly laminations registered and in side-by-side relationship ona support structure thereby forming the stator pole assembly; mountingthe rotor pole assembly laminations registered and in side-by-siderelationship on a support shaft extending through the central aperturesof the rotor pole assembly laminations thereby forming the rotor poleassembly; mounting the support shaft for rotation relative to thesupport structure with the rotor pole assembly positioned centrallywithin and substantially coplanar with the stator pole assembly.
 5. Amethod of making laminations for a stator pole assembly and acooperating rotor pole assembly, comprising:A. providing a plate ofmagnetic material, B. stamping the plate thereby defining an outerperipheral edge corresponding in shape to an outer peripheral surface ofan annular stator yoke; C. stamping the plate thereby defining a centralaperture centered about a center point of the plate; D. stamping theplate thereby defining a multiplicity of apertures of predeterminedidentical shape equally-spaced circumferentially and at a common radialdistance from the center point of the plate, the predetermined shapebeing selected such that the multiplicity of apertures define internaledge surfaces in the plate corresponding in shape to radially innersurfaces of the stator yoke and to radially outer surfaces of a centralhub of the rotor pole assembly and define a multiplicity of identicalradial webs equally-spaced circumferentially; and, E. stamping themultiplicity of webs thereby producing a cut through each web with acommon predetermined radius of curvature relative to the center point ofthe plate such that the plate is divided into a stator pole assemblylamination with radially-inward projections corresponding in shape tostator poles and a rotor pole assembly lamination with radially-outwardprojections corresponding in shape to rotor poles.
 6. The method ofclaim 5 in which:the stamping in step C comprises shaping the centralaperture such that the plate interfits with an indexing element of anindexing table; the stamping in step D comprises providing a punchshaped to produce apertures of the predetermined shape, interfitting theplate with the indexing element of the indexing table and repeatedlyindexing the plate by preselected angular increments about apredetermined indexing axis through the center point of the plate, andproducing a reciprocating rectilinear displacement of the punchsynchronized with the indexing of the plate and directed along an axisparallel to and offset from the indexing axis.
 7. The method of claim 6comprising providing a punch having stamping surfaces corresponding inshape both to the outer peripheral surface of the stator yoke and to thecentral aperture, and performing the stamping in steps B and C with onepass of the punch against the plate.
 8. A method of making laminationsfor a stator pole assembly and a cooperating rotor pole assembly,comprising:providing a plate of magnetic material, stamping the platewith a single pass of a first stamping element thereby defining an outerperipheral edge corresponding in shape to an outer peripheral surface ofan annular stator yoke and a central aperture centered about a centerpoint of the plate having a shape complementary to an indexing elementof an indexing table; mounting the plate on the indexing table with theindexing element operatively located within the central aperture andrepeatedly indexing the plate about a predetermined indexing axis byequal angular increments; stamping the plate with a second stampingelement supported for reciprocating rectilinear movement along an axisparallel to and offset from the indexing axis in response to indexing ofthe plate such that a multiplicity of identical apertures of apredetermined shape are formed in the plate, equally-spacedcircumferentially and at a common radial distance from the indexingaxis, the predetermined shape being selected such that the multiplicityof apertures define internal edge surfaces in the plate corresponding inshape to radially inner surfaces of the stator yoke and to radiallyouter surfaces of a central hub of the rotor pole assembly and define amultiplicity of identical radial webs equally-spaced circumferentially;and stamping the multiplicity of webs therebhy producing a cut througheach web with a common predetermined radius of curvature relative to thecenter point of the plate such that the plate is divided into a statorpole assembly lamination with radially-inward projections correspondingin shape to stator poles and a rotor pole assembly lamination withradially-outward projections corresponding in shape to rotor poles.